Na₃MnTi(PO₄)₃/C Nanofiber Free-Standing Electrode for Long-Cycling-Life Sodium-Ion Batteries

Abstract

Self-standing Na3MnTi(PO4)3/carbon nanofiber (CNF) electrodes are successfully synthesized by electrospinning. A pre-synthesized Na3MnTi(PO4)3 is dispersed in a polymeric solution, and the electrospun product is heat-treated at 750 °C in nitrogen flow to obtain active material/CNF electrodes. The active material loading is 10 wt%. SEM, TEM, and EDS analyses demonstrate that the Na3MnTi(PO4)3 particles are homogeneously spread into and within CNFs. The loaded Na3MnTi(PO4)3 displays the NASICON structure; compared to the pre-synthesized material, the higher sintering temperature (750 °C) used to obtain conductive CNFs leads to cell shrinkage along the a axis. The electrochemical performances are appealing compared to a tape-casted electrode appositely prepared. The self-standing electrode displays an initial discharge capacity of 124.38 mAh/g at 0.05C, completely recovered after cycling at an increasing C-rate and a coulombic efficiency ≥98%. The capacity value at 20C is 77.60 mAh/g, and the self-standing electrode exhibits good cycling performance and a capacity retention of 59.6% after 1000 cycles at 1C. Specific capacities of 33.6, 22.6, and 17.3 mAh/g are obtained by further cycling at 5C, 10C, and 20C, and the initial capacity is completely recovered after 1350 cycles. The promising capacity values and cycling performance are due to the easy electrolyte diffusion and contact with the active material, offered by the porous nature of non-woven nanofibers.

Keywords

• Na-ion batteries
• Na₃MnTi(PO₄)₃
• NASICON-type electrode
• self-standing electrode
• carbon nanofibers